This invention is related to a coating composition which when applied on a fibrous nonwoven sheet of a polyolefin and dried provides a sheet having water barrier, antistatic, and antislip properties and is related to sheets coated with the composition.
Nonwoven fibrous sheets of polyolefins have found utility in a multitude of applications due to their combination of tensile and aesthetic properties at low cost. Some nonwoven fibrous polyolefin sheets display inherent water barrier properties whereas most other nonwoven fibrous sheets of a polyolefin lack appreciable inherent water barrier properties. Nonwoven fibrous polyolefin sheets possessing liquid barrier properties have potential advantages in a variety of applications including disposable protective garments such as surgeons' gowns; protective wrap for various commodities such as carpets, fiber bales, lumber and grain; sterile packaging permeable to sterilizing gases but impermeable to bacteria or liquids; and consumer products such as wind breakers, rainwear and sleeping bag liners.
A decided disadvantage of articles made from nonwoven fibrous polyolefin sheets is the well-known propensity of these articles to accumulate static charges. The conventional technique of simply applying antistat finishes to the nonwoven sheet does not ordinarily lead to a satisfactory solution, since in general finishes which adequately suppress static charge generation simultaneously diminish whatever water barrier property which the nonwoven fibrous polyolefin sheet inherently possessed.
Although the prior art has employed coating compositions which may be applied to various fibrous sheets to impart high water barrier performance thereto, these compositions generally do not simultaneously impart both high water barrier and good antistatic properties. Hydrophobic ingredients are required in order to impart good water barrier performance whereas good antistat materials are commonly hydrophilic. Attempts to combine the two components into a single coating composition ordinarily lead to incompatibility problems in formulation and/or destruction of one or both of the desired effects.
U.S. Pat. No. 3,821,021, issued to McMillin on June 28, 1974, discloses a limited class of finishing agents which can be applied onto certain nonwoven sheets composed of polyolefin film-fibril elements to confer antistatic protection without destruction of the sheets' inherent liquid barrier properties. These finishing agents which are said to possess a balance of high antistat activity and moderate aqueous surfactant power are defined by the formula: M.sub.n R.sub.3-n PO.sub.4 where M is selected from the group consisting of lithium, sodium, potassium, and ammonium ions; R represents an alkyl group containing 3 to 5 carbon atoms, and n is selected from the integers 1 and 2. However, these finishing agents do not impart acceptable water barrier properties to a nonwoven fibrous polyolefin sheet which does not inherently possess an adequate water barrier level.
French Pat. No. 1,207,680 discloses a coating composition which can be used to impart water and grease impermeability to paper materials and which is useful for coating textile materials. The composition comprises an emulsion of polyvinyl acetate; a wax emulsion; a protective colloid for both emulsions, emulsifying agents, which for the wax emulsion can be the esters of the monolaurate, monooleate, and monostearate type known by the name "Spans" (manufactured by Atlas Powder Co.) or the polyoxyethylene derivates of these esters, for example, the monolaurate of polyoxyethylene sorbitan known by the name "Tweens", and optionally a small quantity of pigment. This coating composition does not impart acceptable antistatic properties to the textile materials.
The problem of imparting antistatic properties to polyolefin articles while maintaining or simultaneously improving their water barrier character has also been attacked. For instance, Japanese patent application publication No. 47-8797/1972 discloses a method of providing water-proofing and/or oil-proofing, and antistatic property to hydrophobic fiber goods, such as knitted and woven products, comprising treating one side of the hydrophobic fiber material with a water-proofing and/or oil-proofing agent and treating the other side with a solution of an antistatic agent. Differences in surface tensions are utilized to accomplish the desired result. This technique requires a two-step application of two separate coating compositions and the resulting product exhibits its water barrier and antistatic properties at opposite surfaces.
A need still exists in the art for a single coating composition which when applied to a nonwoven fibrous polyolefin sheet and dried will provide a sheet having both antistatic and high water barrier properties.